The present invention relates generally to apparatus for detecting impurities in a gaseous atmosphere with a corona discharge and more particularly, to a continuously adjusting corona current source.
Apparatus for detecting gaseous impurities, such as halogens, in atmospheres with a continuous corona discharge are known in the prior art. Such devices are known to be sensitive indicators of the presence and concentration of gaseous impurities. Of special interest is the fact that the corona discharge current level diminishes with increasing concentration of halogen gases, since halogen gases possess positive ions, which combine with the negative ozone ions within the corona discharge to decrease the space charge current flow. The recombinations of ions is dramatic in that a large current change occurs for a small concentration of gaseous impurities. As a result of this phenomenon, these devices are capable of detecting halogen gases in very low concentrations. Likewise, the ability to maintain an optimum level of corona current within a constantly changing background level of impurities is highly desirable. To maintain this optimum corona current flow over a long period of time regardless of slowly varying background levels, humidity, air flow, sensing tip variations, electronic components drift, contamination and human adjustment errors requires a continuously adjusting apparatus.
The typical prior art devices used some automatic means to establish an initial adjustment, independent of manual methods, and then assumed this condition to remain stable; or else made timely periodic recalibration setups at fixed intervals.
Since the prior art states that the devices are inherently unstable requiring troublesome frequent recalibration, there were many attempts to resolve the problem.